The problem still exists for me and I am on 6.6.3
I use a multi monitor setting with my MacBook Pro (Model MacBookPro14,2 on macOS Big Sur 11.4). Sometimes Enpass opens semi-transparent as shown in the previous screenshots in this thread. The workaround for me is moving the Enpass window from one screen to the other. That reloads the window and it is non-transparent as it should be.